Fix incomplete LTO bug workaround.

https://android-review.googlesource.com/c/platform/build/soong/+/641827
forgot this use of ClangTriple(), so static libraries aren't being
installed to the correct place.

Test: OUT_DIR=ndk-out DIST_DIR=ndk-dist \
    build/soong/scripts/build-ndk-prebuilts.sh && \
    ls ndk-out/soong/ndk/sysroot/usr/lib
Bug: None

Change-Id: I750ab198deff92aac06935d38d529b53030f9636